This disclosure relates to polycarbonate compositions and particularly to flame retardant polycarbonate compositions.
Polycarbonate resins have been used extensively in the fabrication of business machines and telecommunications equipment due to excellent electrical properties, transparency and mechanical strength, especially impact strength. Business machines and telecommunications equipment are subject to stringent safety requirements, particularly in the area of fire retardancy. These safety requirements are difficult to achieve in thin wall articles, i.e. those with a wall thickness of less than about 2.5 millimeters (mm). Previous attempts to meet safety requirements in thin wall articles include employing polycarbonate with very low melt flow (high viscosity), and using linear polycarbonate combined with high levels of polytetrafluoroethylene or high levels of chlorinated or brominated fire retardants. Each of these approaches has drawbacks, however. Polycarbonates with low melt flow cannot be formed by injection molding. High levels of polytetrafluoroethylene result in translucent compositions with high levels of haze and low transparency, and it is becoming increasingly desirable for safety requirements to be met without using chlorinated or brominated fire retardants.
Thus, it is clear that meeting safety requirements in a translucent polycarbonate composition with low haze and high transparency without the use of chlorinated or brominated fire retardants is a significant challenge, especially in compositions useful in injection molding and/or thin wall applications.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a fire retardant, translucent polycarbonate composition comprising a branched polycarbonate resin, a polytetrafluoroethylene resin, and a fire retardant free of bromine and chlorine; wherein the polycarbonate composition has less than or equal to about 30% haze and greater than or equal to about 70% light transmission at a thickness of about 3.2 millimeters as well as a V1 rating or better at a thickness less than or equal to 2.5 millimeters according to UL 94.
In another aspect, a fire retardant, translucent polycarbonate composition comprises branched polycarbonate resin, polytetrafluoroethylene resin present in an amount less than about 0.10 weight percent based on the total weight of polycarbonate; and a fire retardant free of bromine and chlorine present in an amount of about 0.01 weight percent to about 0.15 weight percent based on the total weight of polycarbonate wherein the polycarbonate composition has a V1 rating or better at a thickness less than or equal to 2.5 millimeters according to UL 94.
In another embodiment, a fire retardant, translucent polycarbonate composition comprises a branched polycarbonate resin; polytetrafluoroethylene; a fire retardant free of bromine and chlorine; and a siloxane wherein the polycarbonate composition has a V1 rating or better at a thickness less than or equal to 2.5 millimeters according to UL 94.
In another embodiment, a fire retardant polycarbonate composition comprises linear and branched polycarbonate resins, polytetrafluoroethylene, a fire retardant free of bromine and chlorine, and a cyclic siloxane.
The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description and appended claims.